This invention relates to a method of controlling a vehicle hydraulic brake system which is provided with a hydraulic pressure source for producing brake hydraulic pressure and in which the hydraulic pressure produced in the master cylinder can also be used as brake hydraulic pressure.
In recent years, in order to realize sophisticated behavior control of the vehicle and get a light brake feeling, as described e.g. in Japanese patent publication 2590825, a vehicle hydraulic brake system is employed in which a hydraulic pressure source for producing brake hydraulic pressure is provided, and a driving device for the hydraulic pressure source is actuated based on a detection signal from a brake operating force detecting means for detecting the operating force of a brake operating member.
Among such hydraulic pressure source-driven type brake systems, there are many in which a master cylinder for producing hydraulic pressure corresponding to the operating force applied to the brake operating member is in communication with wheel cylinders through an on-off valve in a so-called master cylinder passage, and when the hydraulic pressure source is not operating normally, the hydraulic pressure in the master cylinder is transmitted as brake hydraulic pressure by opening the on-off valve to provide a failsafe function.
Among such hydraulic pressure source-driven type brake systems, there are ones in which in order to impart brake feelings of a conventional type brake system to a driver, a stroke simulator for producing mock brake hydraulic pressure is provided in communication with the master cylinder. The stroke simulator has a brake fluid absorbing chamber communicating with the master cylinder and is adapted to produce mock brake hydraulic pressure in the master cylinder by producing a back pressure in the brake fluid absorbing chamber.
With such a conventional hydraulic pressure source-driven type of brake system, even when the vehicle is stopped, while the vehicle driving devices such as the engine or motor is idling, control of the brake system is still carried out. Thus, with brake operations, the driving device for the hydraulic pressure source is still activated. When the vehicle stops and the surroundings become quiet, noises and vibrations resulting from the separation of the driving device irritate people. Also, for the operation of the driving device, electric power is wasted.
An object of this invention is therefore to provide a control method of a hydraulic pressure source-driven type vehicle hydraulic pressure brake system in which no irritating noises or vibrations are not produced during a stop of the vehicle and which does not waste electric power.
According to this invention, there is provided a method of controlling a vehicle hydraulic brake system comprising a brake operating member, a master cylinder for producing hydraulic pressure corresponding to a brake operating force applied to the brake operating member, a wheel cylinder, a hydraulic pressure source for producing brake hydraulic pressure in the wheel cylinder, a driving device for the hydraulic pressure source, a fluid passage bringing the hydraulic pressure source and the wheel cylinder into communication with each other, a master cylinder passage bringing the master cylinder and the wheel cylinder into communication with each other through an on-off valve, a relief passage communicating the master cylinder with the wheel cylinder through an on-off valve, and a brake operating force detecting means for detecting the brake operating force applied to the brake operating member, wherein while the hydraulic pressure source functions normally, the on-off valve in the master cylinder passage is closed, and the driving device for the hydraulic pressure source is actuated based on the detection signal from the brake operating force detecting means, characterized in that a vehicle stoppage detecting means for detecting stoppage of the vehicle is provided, and when the vehicle stoppage detecting means detects stoppage of the vehicle, the driving device for the hydraulic pressure source is stopped and the on-off valve in the master cylinder passage is opened.
That is to say, when the vehicle stops, by stopping the driving device for the hydraulic pressure source of the brake system and and opening the on-off valve in the master cylinder passage to bring the master cylinder and the wheel cylinder into communication with each other as in a conventional type brake systems to transmit the master cylinder hydraulic pressure to the wheel cylinder as brake hydraulic pressure, no irritating noises or vibrations will be produced, and electric power will not be wasted.
By providing a master cylinder hydraulic pressure detecting means for detecting hydraulic pressure produced in the master cylinder, and a brake hydraulic pressure detecting means for detecting the brake hydraulic pressure in the wheel cylinder, and by opening the on-off valve in the master cylinder passage, if the pressure difference between the hydraulic pressure in the master cylinder detected by the master cylinder hydraulic pressure detecting means and the brake hydraulic pressure detected by the brake hydraulic pressure detecting means is below a predetermined threshold, it is possible to prevent sharp reverse flow of brake fluid from the wheel cylinder into the master cylinder, sharp outflow of brake fluid from the master cylinder into the wheel cylinder, a kickback in the brake operating member, or sinking of the brake operating member, all resulting from the opening of the on-off valve in the master cylinder passage.
By opening the on-off valve in the relief valve when the release of the brake operating member is detected by the detection signal from the brake operating force detecting means, or by a detection signal from a separately provided brake operating amount detecting means for detecting the brake operating amount of the brake operating member, it is possible to discharge brake fluid in the wheel cylinder into the relief passage and prevent excess brake fluid from flowing back into the master cylinder from the master cylinder passage. If excess brake fluid flows back into the master cylinder, residual pressure may be produced in the master cylinder after release of brake operation, thus damaging the cup seal of the master cylinder.
By providing a stroke simulator having a brake fluid absorbing chamber into communication with the master cylinder, providing a master cylinder hydraulic pressure detecting means for detecting the hydraulic pressure produced in the master cylinder, a brake hydraulic pressure detecting means for detecting the brake hydraulic pressure in the wheel cylinder, and a brake operating amount detecting means for detecting the brake operating amount of the brake operating member, opening the on-off valve in the relief passage when an operation tending toward release of the brake operating member is detected by the detection signal of the brake operating amount detecting means, and controlling the degree of opening of the on-off valve in the relief passage such that the hydraulic pressure in the master cylinder detected by the master cylinder hydraulic pressure detecting means, or the brake hydraulic pressure detected by the brake hydraulic pressure detecting means becomes a predetermined hydraulic pressure corresponding to the brake operating amount detected by the brake operating amount detecting means, it is possible to prevent excess brake fluid from flowing back into the master cylinder from the master cylinder passage, and get the same brake feeling as during traveling even after stoppage of the vehicle.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: